[R&D Insights] No More Screeching in Rainy Road Cycling: NVH-Driven Silent Brake Pad Development

When braking in rainy conditions on road bikes, that sharp high-frequency squeal often drives riders crazy. Many cyclists assume it's a dirty rotor or low-quality pads, but based on our factory experience, most cases are due to unresolved wet-condition NVH issues. NVH (Noise, Vibration, Harshness) is particularly serious in bicycle braking under rain. A thin water film forms between the pad and rotor, causing a lubrication effect, the friction coefficient μ becomes unstable, and vibration occurs.

We do not simply tweak materials; our process covers materials science, damping design, and dynamic testing step by step, ensuring quiet braking and stable lever feel even in rain. After handling more than fifty rain-noise cases, we found that about 80% originate from water-film issues, while dirty rotors are only a minor factor. This article explains how we approach rainy-condition noise from an R&D perspective, including material selection and wet-condition testing practices.

1. Root Cause of Rain Noise: Water-Film-Induced Stick-Slip
   In dry braking, a stable shear layer forms quickly and force transmission remains smooth. With rain, however, the water film behaves like lubricant, causing instantaneous sticking and slipping (Stick-Slip). Friction force fluctuates rapidly, generating high-frequency vibration that becomes the annoying squeal.
   
   It is not that the pads are too hard or the rotor is dirty—dirty rotors only affect initial bite. The real issue is insufficient water-film breakup, preventing wet friction coefficient μWet from building. Key factors include water absorption, film-breaking capability, and whether the elastic modulus allows effective damping. From our experience, simply adjusting hardness does not work; fiber architecture is the decisive factor.

2. Why Wet-Condition NVH Is Difficult: Multi-Variable Challenges
   Wet NVH is far more complex than dry conditions. Variables include water amount, riding speed, material elastic modulus, and resin glass transition temperature (Tg). From a factory perspective, water-film breakup depends on several raw materials:

   • Inorganic particle size affects film-breaking efficiency
   • Metallic elements assist heat conduction and help maintain friction temperature
   • Fiber orientation and density control vibration transmission

   If resin elasticity is too low, it hardens at lower rain temperatures and amplifies noise; an uneven fiber network results in unstable vibration frequencies. Many commercial pads are quiet in dry conditions but squeal in rain. Our data also shows higher occurrence in road bikes compared to e-bikes or MTB; road bikes show the most severe rain-noise incidence.

3. Three Key Design Logics for Silent Pads: Materials, Damping, Fiber Network
   To achieve rain-quiet performance on road bikes, our design follows three aspects: water-film breakup, resin damping with high-frequency suppression, and fiber-network control.
   
   For water-film breakup, we use inorganic particles and fibers that absorb water and break the film quickly on first contact, reducing Stick-Slip. Through repeated testing, we found that simply increasing a certain ingredient does not guarantee quieter performance; resin ratios must maintain elasticity under humid, low-temperature conditions to absorb high-frequency vibration.
   
   Finally, the fiber network uses a mix of long and short fibers, cross-oriented, with moderate density to avoid vibration amplification. These are not standard public formulas; we iterated over hundreds of trials based on ODM experience.

4. Wet μ: The Core Metric of Silent Performance
   Reducing noise does not mean blindly increasing friction. The goal is minimizing μ difference between wet and dry and building the curve faster. About 95% of rain squeal comes from large μ fluctuation. We target the smallest μWet–μDry gap, achieving stable curve buildup within 0.5 s.
   
   Using dynamic friction curve simulation, we focus on stability in both dry and wet conditions. This not only reduces noise but ensures linear lever feel without sudden variations. Many brands overlook this NVH principle and fail in rainy tests.

5. Simulated Rainfall Testing: Practical Factory Workflow
   Theory alone is insufficient. We perform wet NVH testing on dynamometers to simulate rainy environments. Conditions include water-spray angle at 45°, flow 15–40 mL/min, temperature 10–30°C, and a minimum duration of 30 minutes.
   
   Modes include constant-speed braking and noise measurement under different lever forces. We measure dB noise, deceleration curves, Stick-Slip waveforms, and recovery times. For example, a recent formula reduced rain noise from 105 dB to 90 dB with smooth μ buildup. This is not a typical commercial procedure; we developed our own protocols to ensure consistent wet-performance across batches.

6. Real-World Rain Ride Testing: From Lab to Road
   After lab approval, field testing is mandatory. We work with professional riders in rainy seasons, focusing on long-descent drag braking—where noise is most likely. Test routes include wet corners, downhill braking, emergency stops, and extended rainy rides.
   
   Results show our pads kept noise below 95 dB during rainy descents, while ambient background is already around 90 dB. Compared to commercial products, mud and water have less influence because our fiber network filters debris effectively.
   
   Lab results always differ from real bikes, so we install dB meters and run 360° video to record braking decibels objectively, rather than relying on perception. We also test different bikes, with road bikes and MTBs showing the largest noise differences.

7. Wet NVH Must Ensure Linear Control, Not Just Silence
   Many pads perform fine in dry but fail in rain because μ buildup is unstable and Stick-Slip remains. True quiet braking must retain μ linearity under wet conditions. Otherwise lever feel becomes unpredictable and potentially unsafe.
   
   We design damping to narrow vibration-frequency ranges and avoid amplification, applying full NVH engineering rather than relying on single-material solutions.

8. Why We Can Achieve Rain Silence: Factory-Level Advantages
   Unlike brands relying on generic formulations, we are an ODM/OEM manufacturer controlling raw materials, process parameters, and formulations. Advantages include in-house development, simulation equipment, wet-spray testing, test riders, and OEM background.
   
   We even control particle size and granularity, which many competitors cannot. This provides a clear advantage in high-humidity, high-rainfall regions, strengthening brand value.

9. Shifting Brand Value: From Braking Power to NVH Confidence
   Many brands emphasize braking power, wear resistance, or ceramic formulas. In road bikes, the real priorities are stability, low noise, fast recovery, and wet-linear control. NVH performance defines user experience. We are not just selling brake pads; we are selling confidence—silent braking in rain so riders can focus on the road.

10. Who Should Use Our Silent Solution?
    Road-bike brands, OEM manufacturers, and high-end component makers, especially in rainy regions such as Taiwan and Japan. Products requiring quiet braking performance can achieve immediate differentiation. Regions with frequent rain benefit the most.

11. Conclusion: Rain Silence Is the Core NVH Differentiator
    Rain noise has little to do with hardness, friction, or rotors themselves; it is fundamentally a wet-condition NVH issue involving water-film breakup, Stick-Slip control, μWet buildup, damping, and fiber networks. Under variable outdoor conditions, this determines brand competitiveness.
    
    Our goal is to build complete NVH capability for brands, making braking a symbol of safety rather than a problem. For brands aiming at true premium road-bike braking, rain-quiet performance is essential. We welcome further discussion and can share data or customized formulations.